What's the difference between the different Rig Types ? (Rigify add-on)
Rig Types are the Properties Collection used by Rigify to identify
  what kind of rig the user is building.


Choice should depend on what controls you want to get for your bones.

Rig types description is in link below.

https://archive.blender.org/wiki/index.php/Extensions:2.6/Py/Scripts/Rigging/Rigify/#Rigify_Rig_Types